Gas generating assembly



June 28, 1960 J w, RABERN ETAL 2,942,547

GAS GENERATING ASSEMBLY Filed June 24, 1958 FIG-2 IN V EN TOR-V.

A m RW f m W m N r H A A @m w $05 JN GAS GENERATING ASSEMBLY JosephWilliam Rabern, Herrin, and Norman J. Wilkaitis, East Alton, Ill.,assignors to Olin Mamieson ChemicalCorporation, East Alton, 11]., acorporation of Virginia Filed June 24, 1958, Ser. No. 744,253

'3 Claims. (Cl. 102-39) This invention relates to gas gen'erating'unitsand par ticularly to improved ignition assemblies therefor.

Solid gas generating charges are generally. used as the source of powerfor the operation of prime movers such as internal combustion engines,motor starters, switch closers, jet engine starters, and" the like.Ain'- monium nitrate with plastic binders has been regarded as the mostsuitable gas generating material in such charges because of its lowcost, ease and safety in handling, and the predictability and control ofgases generated upon ignition. However, ammonium nitrate consolidatedcharges are exceedingly difiicult to ignite. Therefore, previousattempts to utilize ammonium nitrate in sol-id gas generating chargeshas not been completely satisfactory because no reliable means hasheretofore been found for their ignition. Ideally, such solid gasgenerating charges develop gas and pressure in a more or less step- Wisemanner. Thus, the initial power generation must be suiti'ciently greatto overcome the inertia of the driven mechanism but at the same time notso great as to destroy the mechanism or subject it'to undue mechanicalforce before his put in motion. After the initial inertia of the drivenmechanism is overcome, the power demands from the gas generating chargeare much greater. Prior art generating devices have been quite deficientin their capability of providing a relatively low pressure followed by asustained substantially constant higher pressure, and this recognizeddesirable result could not be reproduceably obtained. 4 v

It is, therefore, an object of this invention to provide a gasgenerating cartridge and an ignition means therefor overcoming thedisadvantages of the prior art. Another object of this invention is toprovide an improved ignition assembly for solid gas generating charges.A more specific'object of this invention is to provide a solid gasgenerating assembly capable of reliably igniting am monium nitrate typegas generating charges as well as other types of gas generating chargesin a stepwise manner. Other objects will be apparent whenthe followingdetailed description is read in connection with the accompanying drawingin which:

Figure 1 is a longitudinal sectional view of a gas generatingcartridgeillustrating a preferred embodiment of the present invention; and

'Figure 2 is a transverse view partially in section taken along'the'lines IIII of Figure 1. g

The objects of the present invention are achieved, gen erally speaking,by providing a cylindrical resilient cartridge case having'a closed endand a discharge port at the other end, and containing a consolidated gasgenerating charge having a longitudinal perforation together with meansto insure positive and'stepwise' ignition of the gas generating chargeover a Wide temperature range. More specifically,the present inventioncontemplates a cylindrical consolidated gas generating charge or grainprovided with a centrally located longitudinal perforation and anignition system for the grain; One portion of the Patented June 28, 1960ignition system for the grain consists of a consolidated ignition orpyrotechnic charge located within the perforationof the grain and nearthe discharge port. In addition, an electric squib imbedded in anigniter assembly is centrally positioned at the other end of theperforation and a plurality of auxiliary ignition pellets are providedbelow the'main fuel charge near the closed end of the cartridge.

The gas generating charge of the present invention is preferablycontained in a resilient casing which is adapted upon ignition of thecharge to expand so as to effectively seal the breech structure or othermechanism in which the cartridge is fired. Various types of syntheticrubber and elastomers can be used in this connection. When such anorganic casing is used, it is preferably provided with'a'n insulatinglining such as asbestos or the like and also with a reinforcing liningof metal or other suitable material. Alte'rnately, a metallic casing canbe used. One end ofthe casing is closed and'carries the necessaryelectrical contacts, while the opposite end constitutes the dischargeport. The discharge end is spanned by a screen or a perforated metalplate to permit passage of the gases interior of the chamber but is of aslightly smaller diatrn. eter' so as to provide an annular space aboutthe periphcry of the grain. This annular space, which is essentialfor'theproper combustion of the grain, is maintained by any suitablespacing means. The end surfaces of the ammonium nitrate charge areinhibited by any converttional means to prevent end burning. Thus, alayer of a non-combustible material, such as rubber-asbestos, am: moniumoxalate-synthetic rubber, epoxy resins, polyurethane, or the like, canbe afiixed to the end surfaces of the grain for this purpose.

The ignition stimulus for the system originates from an electric squibor similar deflagrating device embedded in a body of a vigorous ignitioncomposition. This ignition composition in which the squib is embedded ispreferably contained in a plastic cup which, upon ignition,disintegrates without forming any harmfulresidue. While polyethylene isparticularly well suited for this purpose, any other suitably evanescentmaterial can be used. The plastic cup is centrally located near theclosed end of the cartridge and is aligned with the central perforationof the main fuel charge. The top of the cup is provided witht a closurethat will readily yield upon ignition of :the contents of the cup. Thetop portion of the cup is directed into the central perforation of thegrain and preferably extends partially thereinto:

' For convenience and clarity in describing the invention, the term topis applied'to the discharge end of the cartridge and the term bottom isapplied to the closed end. It will, of course; be readily apparent thatthis cartridge can be fired in any position.

Various types of ignition compositions capable of pro ducing an intenseflame with a moderate evolutionof gaseous products can be'utilized inthis plastic cup. These charges are preferably provided with a binder;Compositions containing'a metal, a plastic binder, and an oxidizer areparticularly well suited for this purpose. .Co'mposie tions containingpolyvinyl acetate, boron, and potassium perchlorate have been found tobe satisfactory but'othei 3 metals, including aluminum and the like,fuels and oxidizers can, of course, be used.

The ignition composition contained in the plastic cup is augmentedbyanignition pellet located in the central perforation of the grain remotefrom the squib and a plurality of cakes of fast burning propellentlocated about the plastic cup at the closed end of the cartridge. Theseauxiliary ignition cake charges are preferably a composi-, tion madewith a rubber type binder, similar to a fast burning rocket propellent.The pellet ignition charge positioned within the perforation of thegrain is preferably contained in a plastic holder and is provided withan inhibitor to restrict burning on the cylindrical surface 4 a of thepellet except for a portion near the open end of the plastic holder.

In order to more vention, reference is made to the drawing for apreferred embodiment thereof. Unless otherwise specified, compositionsof the various formulationsare expressed in parts by weight. In thisembodiment, the body of the cartridge consists of a synthetic rubbercasing :1, the sidewalls of which are provided with a liner 2 ofasbestos and a metallic reinforcing liner 3. The closed end of thecartridge is dome shaped, as indicated generally at 4 and the opposingdischarge end is closed by a perforated plate or screen 5, which iscrimped about the lower end of the cartridge as shown at 6. A thin layer7 of polyester plastic tape or other evanescent plastic material ispositioned over screen to provide a weather seal for the cartridge. Themain fuel charge is a consolidated grain 8 of granular ammonium nitratein a binder of polybutadiene acrylic acid type synthetic rubber. Thisgrain is provided with a layer of inhibitor 23 at each end to insurelateral burning. The grain is maintained in position within thecartridge by plastic spacers 9 which are integral with lateralextensions 10 of centrally located support 11. Metallic supports 12cooperate with plastic members 9 to maintain the grain in alignment.These members extend from the central portion of the closed end of thecartridge to the top of the gas generating grain. The electricalcontacts forinitiation of the squib pass through the closed end of thecartridge and are shown generally at 13. Squib 14 is provided with leadwires 15 and is embedded in a black powder-pyrotechnic mixture 16 havingthe following approximate composition:

8.5% powdered boron 78.5 potassium perchlorate 8.0% graphite 5.0%polyvinyl acetate In addition, the assembly is also provided with fourcast propellent charges or cakes 22 which are bonded to supportingmembers 12 and positioned radially toplastic cup 17 between the maingrain and the closed end of the cartridge. Two of these four pressedcharges were composed of a mixture of about 75.0% ammonium perchlorate,12.5% polyvinyl chloride, and 12.5% dioctyl phthalate, while theremaining two charges were composed of boron aluminum potassiumperchlorate graphite polyvinyl acetate fully explain and clarify the ina mixture of about 57.5% potassium perchlorate, 12.5% aluminum powder,5% boron, 12.5% dioctyl phthalate, and 12.5 polyvinyl chloride. In thoseinstances where it is desired that these charges be aluminum free, theremaining two cast propellent cakes can be composed of a mixture ofabout 12.5% dioctyl phthalate, 12.5% polyvinyl chloride, 1% boron, and74% potassium perchlorate.

Upon firing the cartridge, squib 14 ignites ignition charge 16 whoseflame is directed through the central perforation of the gas generatingcharge so as to impinge upon the exposed surface of igniter pellet 20.Charge 20 then ignites vigorously and together with the action of charge16 initiates combustion of the gas generating charge 8 on its surface onthe central perforation 19. Auxiliary ignition charges 22 are thenignited and assist in carrying the flame and hot gases to the peripheralsurfaces of the ammonium nitrate grain. In operation, the elastomericcase '1 is readily expanded so as to avoid any gas leakage or blow-backin the breech mechanism or cartridge holder which is not shown and doesnot form a part of the present invention. The plastic covering 7 for theforaminous closure plate 5 ruptures or burns so as to provide readyegress for the gaseous combustion products.

The ignition of the main gas generating charge in its centralperforation by substantially non-gaseous ignition charges followed byignition of the outer surface of the grain provides 'a system whereinthe initial pressure generated by the cartridge is relatively low and isfollowed by a sustained period of substantially high pressuregeneration.

While the above embodiment was directed specifically to an ammoniumnitrate type gas generating charge, it will be readily appreciated thatthis ignition system can be utilized with advantage in connection withother gas generating compositions based on nitroguanidine, guanidinenitrate, perchlorates, and the like. It is also evi dent that variousother modifications may be made without departing from the scope of thepresent invention. For example, various types of ignition compositionscan be used. Also, the ignition pellet contained within the centralperforation can be uninhibited and a larger or smaller number ofauxiliary ignition charges can be positioned between the gas generatingcharge and the closed end of the cartridge. Also, the ignition assemblycan be housed and positioned by any suitable means.

Since variations in the specific embodiment may be made within thespirit and scope of this invention, the detailed description is not tobe considered as limitative except in the light of the appended claims.

What is claimed is:

1. A gas generating cartridge for an engine starter and the likecomprising a substantially cylindrical resilient casing having apermanently closed end and an oppositely disposed discharge end, acentrally perforated substantially cylindrical end-inhibited ammoniumnitrate gas generating charge disposed in and spaced from the casing asthe main charge, the longitudinal axes of the cylindrical casing and ofthe cylindrical gas generating charge being substantially parallel, alaterally and basally inhibited cylindrical pyrotechnic chargepositioned in and substantially filling that portion of the centralperforation proximate the discharge end of the cartridge, the base ofthe pyrotechinc charge being proximate the discharge end of thecartridge, an electric squib embedded in an ignition mixture, saidignition mixture being contained in an evanescent plastic cup positionedat the closed end of the cartridge and having'a portion extending intoand substantially closing that portion of the central perforationproximate the closed end of the cartridge, and a plurality of ignitioncharges positioned radially about the plastic cup and between the closedend of the cartridge and the proximate end of the ammonium nitrategrain.

2. A gas generating cartridge for an engine starter and the likecomprising a substantially cylindrical resilient casing having apermanently closed end and an oppositely disposed discharge end, an endinhibited gas generating centrally perforated grain contained in thecasing and spaced therefrom, an evanescent cup positioned at one end ofthe perforation with a cylindrical portion of the cup extending into andclosing that end of the perforation, the evanescent cup containing anignition mixture having an electric squib embedded therein, the oppositeend of the perforation being closed by a pyrotechnic charge free to burnonly on that surface facing the evanescent cup, and a plurality ofignition charges positioned radially about the plastic cup and betweenthe closed end of the cartridge and the gas generating grain.

3. A fuel charge for a gas generating device comprising as the main fuela cylindrical end-inhibited grain of a gas generating composition havingat least one longitudinal perforation, a laterally and basally inhibitedcylindrical pyrotechnic charge substantially filling one end of theperforation in the gas generating charge, the top of the pyrotechniccharge extending into the perforation, an ignition assembly closing theother end of the perforation and containing an electric squib embeddedin an ignitor mixture contained in an evanescent plastic cup, aplurality of ignition charges positioned radially about the ignitionassembly and between the perforation and the external wall of thecylindrical grain, and means supporting said grain and charges.

References Cited in the file of this patent UNITED STATES PATENTS2,518,958 Thompson et al Aug. 15, 1950 2,685,837 Sage et a] Aug. 10,1954 2,688,920 Jarvis Sept. 14, 1954 2,743,580 Loeb May 1, 19562,771,035 Clark Nov. 20, 1956 2,865,456 Dennis Dec. 23, 1958 FOREIGNPATENTS 502,757 Germany Aug. 5, 1930 OTHER REFERENCES Jet Propulsionmagazine article, Feb. 1956, pp. 102 and 103 required.

